The present invention relates to a filler-incorporated thermoplastic resin composition and more particularly to a thermoplastic resin composition well-balanced in rigidity, resistance to impact and to heat, dimensional stability, flame retardance and moldability, prepared by incorporating an inorganic filler and/or a flame retardant into a thermoplastic resin composition containing a partially crosslinked product obtained by dynamically heat-treating a thermoplastic resin and/or a rubbery substance using a specific crosslinking agent.
Heretofore, for the modification of a thermoplastic resin composition, that is, for the purpose of improving rigidity, dimensional stability and flame retardance, it has been well known to incorporate and inorganic filler and a flame retardant into a thermoplastic resin.
For example, general-purpose synthetic resins typified by polyethylene are disadvantageous in that they are poorly receptive of inorganic fillers and inorganic flame retardants and that if fillers are incorporated in a large amount into those resins for the purpose of improving rigidity and heat resistance or flame retardancy of the resins, the mechanical strength, flexibility and processability of the resulting resin compositions will be deteriorated to an unpractical extent.
Thus, there is a limit on the amount of fillers capable of being used; that is, a limit is encountered in attaining a high modification effect.
Further, thermoplastic resins have the drawback that they are easy to burn because of organic compounds. Besides, their burning energy is very powerful, thus giving rise to great danger in the event of a fire. In view of this point there have been proposed methods for making thermoplastic resin compositions flame-retardant.
According to the most general method among them, organic polymers can be rendered flame-retardant by incorporating therein flame retardants containing halogen or phosphorus.
However, these organic flame retardants have a serious drawback of evolving noxious gases when they burn.
Recently, flame-retardant compositions have been required to be more highly flame-retardant from the standpoint of preventing a fire.
Under the circumstances, as low-smoking, pollution-free flame retardants not evolving noxious gases during burning unlike organic flame retardants, inorganic flame retardants such as magnesium hydroxide and aluminum hydroxide meet the aforementioned needs and are now in increasing demand rapidly (see, for example, Japanese Patent Laid Open No. 13832/1985).
The degree of flame retardance attained increases with increase in the amount of such inorganic flame retardants used.
On the other hand, the increase in the amount of inorganic fillers and inorganic flame retardants results in not only deteriorated mechanical strength and processability but also marked impairment of flexibility and cold resistance.
To maintain those properties in satisfactory condition there been proposed the use of polymers having polar groups highly receptive of fillers, the use of a soft substance (e.g. rubber) for retaining flexibility, or the use of a soft substance as matrix itself.
However, in the use of a filler in a large amount, a mere incorporation therein of a small amount of a soft substance will be poor in the effect of improving the mechanical strength, etc. thereof, so it becomes necessary to use a soft substance in a large amount, thus causing deterioration in the heat resistance of the resulting composition.
To improve the heat resistance of the resin composition such soft substance incorporated therein, there generally is adopted a crosslinking means for the composition.
Usually, in a crosslinking reaction there is adopted a method which employs a free radical forming agent typified by an organic peroxide. However, organic peroxides involve the following problems because of high activity thereof.
For example, in the case of using a peroxide disintegrating type thermoplastic resin such as polypropylene, there is obtained a composition having high fluidity, while on the other hand since there rapidly occurs thermal decomposition of the organic peroxide used, a molecule cutting reaction is unavoidable, thus causing deterioration in mechanical strength such as rigidity and yield tensile strength.
In the case of using a peroxide crosslinking type resin such as polyethylene, a crosslinking reaction will proceed to an extreme degree, thus causing marked deterioration of fluidity, with the result that the moldability is deteriorated to an extent of molding being difficult, and in order to retain good moldability it is necessary to use a very small amount of an organic peroxide, so the handling thereof is difficult (see, for example, Japanese Patent Laid Open Nos. 10 47/1975, 23244/1974 and 102 6/1974).
Further, the organic peroxide remaining in the composition deteriorates thermal stability and weathering resistance.
Thus, in both the above method of performing a crosslinking reaction using a peroxide and the above method using a soft substance, deterioration of mechanical strength is unavoidable.
Other problems involve a problem in management relating to the stability and safety of a peroxide during storage, and a thermal decomposition loss caused by the adhesion of a peroxide to the walls of a heated processing machine. It has been desired to solve these problems.
Thus, none of conventional thermoplastic resin compositions with fillers such as inorganic filler and/or flame retardants incorporated therein are fully satisfactory in practical use, and so it has been desired to provide an improved composition.